The present disclosure relates to a marking device, in particular a developer camming apparatus for a two-pass, multi-color electrophotographic printer, and to a method of two-pass multi-color electrophotographic printing using a developer camming apparatus.
The developer camming apparatus of the present disclosure allows a document to be printed without the need of a developer unit contacting a photoreceptor in order to apply toner. Further, each developer unit contains a developer camming apparatus, which provides each developer unit independent positioning control allowing each developer unit the ability to move in opposite directions of each other, that is, toward the photoreceptor or away from the photoreceptor, with independent timing.
The methods and apparatus herein thus have utility in eliminating transient force placed on the photoreceptor, thereby improving motion quality and image quality.
Electrophotographic marking is a well-known and commonly used method of copying or printing documents. Electrophotographic marking is performed by exposing a light image representation of a desired document onto a substantially uniformly charged photoreceptor. In response to that light image, the photoreceptor discharges so as to create an electrostatic latent image of the desired document on the photoreceptor's surface. Toner particles are then deposited onto that latent image so as to form a toner image. That toner image is then transferred from the photoreceptor onto a substrate such as a sheet of paper. The transferred toner image is then fused to the substrate, usually using heat and/or pressure. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image.
Electrophotographic marking produces color images by repeating the above process once for each color of toner that is used to make the composite color image. For example, in a one-color process, a charged photoreceptive surface is exposed to a light image, which represents a first color, for example black. The resulting electrostatic latent image is then developed with black toner particles to produce a black toner image. For multi-color processes, the charge, expose, and develop process is repeated for a second color, for example yellow, then for a third color, for example magenta, and finally for a fourth color, for example cyan. The various color toner particles are placed in superimposed registration so that a desired composite color image results. That composite color image is then transferred and fused onto a substrate.
The above process can be implemented in various ways. For example, in a two-pass marking device, the composite final image is produced in two-passes of the substrate by the photoreceptor through the machine where only one color toner image is produced during each pass by the photoreceptor through the marking device. A second implementation may be a four-pass printer where only one color toner image is produced during each pass by the photoreceptor through the machine.
Typical developer units include camming mechanisms that bring each developer unit into contact with spacers that are set between the developer and the photoreceptor at a predetermined distance. However, contact with the photoreceptor may produce transient force causing the photoreceptor to bend, which affects motion quality and image quality. Current developer camming mechanisms attempt to solve this problem by either 1) minimizing the force placed on the photoreceptor by a developer unit, that is, the force applied to a photoreceptor is minimized as a developer unit makes contact with a spacer, or 2) keeping the force placed on the photoreceptor constant, that is, just as one developer unit starts to move away from a spacer and the photoreceptor, another developer unit moves into contact with a spacer that is between the photoreceptor and the developer, thus maintaining a constant force against the photoreceptor.
However, as mentioned above, developer camming mechanisms may cause transient force to a photoreceptor, and therefore affect motion quality and image quality.